1. Field of the Invention
This invention relates to an improvement in an extendible nozzle exit cone for rocket motors.
2. Description of the Prior Art
Deep space ballistic missile systems or satellite probes require high performance, low weight, and highly packageable primary propulsion systems. Excluding propellant tanks, the largest component of the propulsion system is the rocket engine exhaust nozzle. The rocket nozzle takes up a large amount of valuable space relative to its mass.
The exit cone for a conventional nozzle for rocket motors is designed for optimum performance at the median altitude of the intended trajectory. One of the functions of the exit cone is to provide an inclined surface against which the expanding exhaust plume of the rocket can bear, thereby to provide some of the forward thrust of the rocket. The exhaust plume grows larger with increasing altitude of the rocket because of the lower pressures of the ambient atmosphere at the higher altitudes. At low altitudes, the exhaust plume is too small for the available surface of the exit cone. As as result, a partial vacuum tends to form on the inside edges of the exit cone, thereby creating an atmospheric drag on the rocket. At high altitudes, the exhaust plume is too large for the exit cone so that much of the potential energy is unused. A rocket motor nozzle that is sufficiently large to make full use of the expanding exhaust gases of a rocket engine in the low ambient pressures at high altitudes would normally occupy an inordinately large proportion of the available storage space in silos, submarines, and between stages of a plural-stage missile.
Thus, there is a need and a demand not only for a rocket motor nozzle exit cone that is capable of providing uniformly high performance over the entire range of the intended trajectory but which also adequately meets the expansion ratios required for high altitude rocket flight while still remaining within length limiting constraints.
Various proposals have been made in the prior art to provide a large expansion ratio nozzle that can be stowed in a collapsed or nested configuration and thereby made to fit in a minimal storage space, and that can be extended to a configuration suitable for high altitude operation after motor ignition and lift off. These have included the use of: (a) a rocket nozzle exit cone extension that is flexible and can be expanded or compressed in various ways as by convoluting, as disclosed in U.S. Pat. No. 3,346,186 to D. L. Fulton et al, U.S. Pat. No. 3,358,933 to J. H. Altseimer, U.S. Pat. No. 3,711,027 to L. F. Carey, and U.S. Pat. No. 3,784,109 to J. W. Dueringer, and in copending application for U.S. Patent bearing Ser. No. 338,713, filed Jan. 11, 1982 by Frank S. Inman and Joseph E. Pelham; (b) an inflatable and convoluted fabric rocket nozzle exit cone extension as disclosed in U.S. Pat. No. 3,596,465 to T. O. Paine et al; and (c) a rocket nozzle exit cone extension that is segmented longitudinally as disclosed in a paper entitled "Nested Extendible Exit Cone Solid Rocket Nozzle Engineering Evaluation Program" presented at the AIAA/SAE 14th Joint Propulsion Conference, Las Vegas, Nevada, July 25-27, 1978, and as disclosed in copending application for U.S. Pat. bearing Ser. No. 230,939, filed on Feb. 2, 1981 by Frank S. Inman; said last mentioned copending application and that mentioned hereinbefore being assigned to the assignee of the present invention.
The present invention is concerned particularly with that form of extendible rocket nozzle exit cone which is segmented longitudinally, and is characterized by its provisions for the automatic translation and deployment, upon command, of the exit cone segments, with a positive drive force, with the system locked against thrust forces of the nozzle, and gas tight seals provided between the segments, as they are aligned in extended position. The invention is further characterized in that less stowage volume is needed for the collapsed and stowed exit cone than for convoluted or folded exit cones.